This invention relates to liquid ring pumps, and more particularly to two-stage liquid ring pumps with rotating housing liners.
Liquid ring gas pumps are well known, as shown, for example, by Haavik U.S. Pat. No. 4,323,334. The typical liquid ring pump includes a stationary annular housing in which a rotor having radially outwardly extending blades is mounted for rotation about an axis which is eccentric to the central longitudinal axis of the housing. A quantity of pumping liquid is maintained in the housing so that when the rotor is rotated, the blades of the rotor engage the liquid and form it into a recirculating ring inside the housing. Because the housing is eccentric to the rotor, the inner surface of this liquid ring alternately moves radially out from the rotor axis and then back in toward the rotor axis in the circumferential direction around the pump. Accordingly, the working spaces between adjacent rotor blades alternately expand (where the liquid which partly fills the spaces between those blades is moving radially out from the rotor axis) and contract (where the liquid between those blades is again moving inward toward the rotor axis) in the circumferential direction around the pump. Gas to be pumped is communicated to the expanding working spaces and the expansion of those spaces pulls the gas into the pump in the so-called intake zone of the pump. The subsequent contraction of the working spaces compresses the gas in those spaces in the so-called compression zone of the pump. The contracted working spaces then communicate with a pump discharge whereby the compressed gas exits from the pump. Liquid ring pumps may be used either as vacuum pumps or as compressors.
Two-stage liquid ring pumps are known in which the gas discharged from a first stage is conveyed to the intake of a second stage for further compression. For example, a typical two-stage liquid ring vacuum pump may be used to produce a reduced pressure of about 1" HgA at its first stage inlet. The first stage outlet and second stage inlet may be at about 4" HgA. The second stage outlet may be at atmospheric pressure (approximately 30" HgA). Exemplary two-stage liquid ring pumps are shown in Haavik U.S. Pat. Nos. 4,323,334 and 4,334,830.
An important source of energy loss and therefore inefficiency in liquid ring pumps is fluid friction between the rotating liquid ring and the stationary housing. One way to reduce such fluid friction loss is to include a rotatable liner between at least a portion of the liquid ring and the inner surface of the housing which would otherwise be in contact with that portion of the liquid ring (see, for example, Kollsman U.S. Pat. No. 2,609,139 and Haavik U.S. Pat. No. 5,100,300). The liner typically rotates at a speed which is a significant fraction of the speed of the liquid ring. The fluid friction loss between the liquid ring and the liner is therefore less than the fluid friction loss would have been between the liquid ring and the stationary housing. While such liners may be supported in other ways (e.g., on mechanical bearings), in the presently preferred pumps, the liners are supported on a fluid bearing in an annular clearance between the liner and the housing.
In order to ensure that a liner of the type described above is adequately supported for rotation by a fluid bearing, the bearing fluid should be at a pressure greater than the gas pressure differential in the associated portion of the pump. This gas pressure differential has the effect of pushing the liner out of concentricity toward the housing on the higher pressure side of the pump. In order to provide bearing liquid at a sufficiently high pressure, it may be necessary to augment the liquid ring pump with a separate pump for pressurizing the bearing fluid (e.g., a liquid pump for increasing the pressure of a portion of the pumping liquid which is introduced into the annular clearance between the liner and the housing as a bearing liquid for the liner). Such additional equipment tends to increase the cost and decrease the reliability of the liquid ring pump installation.
In view of the foregoing, it is an object of this invention to improve and simplify liquid ring pumps with rotating liners.
It is a more particular object of this invention to eliminate or at least substantially reduce the need for a separate pump for the bearing fluid which supports the rotating liner in at least some liquid ring pumps.